From German Patent No. DE 199 00 740, a method for controlling an engine is known in which the correct functioning is monitored as well. In the process, it is checked whether the signal from a lambda probe, i.e. a probe representing the oxygen concentration of the exhaust gas of the internal combustion engine, exceeds a predefined limiting value. Such limiting values are to be controlled especially when a lean air/fuel mixture is given.
The method according to the present invention and the device according to the present invention have the advantage that a monitoring of the correct functioning is possible even in the case of internal combustion engines which have no sensor for determining lean operating states. Therefore, the method and the device according to the present invention may be uniformly used both for engines that are continuously operated at lambda=1, and for engines in which a deviation from a value of lambda=1 is possible in certain operating states. The present invention ensures that one and the same monitoring of the correct functioning is made possible in a uniform manner for both types of engines, thereby allowing uniform use of the present invention for different engine concepts.
The present invention, in particular, is able to be utilized in a useful manner in engines in which the injected fuel quantity is controlled to a lambda setpoint value, especially in engines in which the lambda setpoint value is controlled to 1. Further influencing factors, such as fuel tank venting or a transition compensation, may be taken into account for calculating the fuel quantity. Additional checks can increase this functional reliability even further. In particular, the calculated control (triggering) time for a fuel injector may be compared to the fuel quantity, thereby ensuring that the control time for the fuel injector is calculated correctly. By comparing a first torque directly calculated from the position of the accelerator pedal, to a torque calculated from the fuel quantity it is possible to determine whether the fuel quantity has been calculated correctly. A further fault check may be performed by comparing a correction value, which is used to convert a setpoint torque into a fuel quantity, to a comparison value. Only predefined deviations from the comparison value are permitted in this context.